The invention relates to a means for cooling a high temperature furnace. In particular, the invention is directed to a probe device useful for cooling furnaces that operate at extremely high temperatures.
Boron carbide and titanium diboride are examples of materials used in high temperature applications, such as refractories, nuclear reactor control rods, high temperature electrical conductors, etc. Materials of this type are made in electric furnaces that operate at temperatures above 1000.degree. C. The furnaces are usually insulated with carbon-based materials, such as lampblack, and they are filled with an inert gas, such as argon.
The severe temperature environment inside the furnace prevents use of metals or metal alloys as materials of construction for various furnace components, such as the heater boards, the roof and floor of the hot zone, the product boats, etc. Under these conditions metals suffer from creep, oxidation, and loss of strength. The common ceramic materials are also unsuitable for this purpose, in that they have very poor thermal conductivity and they tend to become brittle under heat stress. For most of the high temperature furnaces now in use the components are made of graphite.
Because these furnaces must operate at such high temperatures, they require an unusually long time to cool down to a temperature where they can be serviced. For example, it can take as long as 125 hours to cool down a typical carbon-insulated furnace that operates at 2200.degree. C.
Equipment now available for cooling high temperature furnaces leaves much to be desired. On of the known devices consists of lengths of metal tubing joined together to form a cooling "loop". The loop is installed in a fixed location inside the insulation section of the furnace. A cooling fluid (gas or liquid) is circulated through the tubing and the absorbed heat is passed to the atmosphere through a cooling tower, or other means. The cooled fluid is then recycled back through the tubing loop in a continuous operation.
One of the problems with this cooling device is that the metal tubing can't tolerate temperatures above about 800.degree. C., because it will carburize or oxidize. Another problem is that the tubing loop must remain in a fixed location, so that it is constantly exposed to the high temperature environment. These limitations make it necessary to place the tubing loop at a location fairly remote from the hot zone of the furnace, so that the cooling effect it has is quite marginal.